In HPLC, a sample to be examined must be fed into a high-pressure liquid flow, wherein the latter must be interrupted only for as short a period of time as possible. For this purpose, high-pressure injection valves are used which permit a virtually interruption-free switch of the liquid flow. Such a design is described for example in U.S. Pat. No. 3,530,721 A.
Injection valves used at present have at least four ports in order to permit sample pre-compression by way of a sample delivery device. An additional port is required if it is sought to dispose of solvent contained in the sample delivery device, or of an incorrectly taken-in sample, via a waste port (disposal port) connected to the injection valve. A sampler having a corresponding injection valve is already described in DE 10 2008 006 266 A1.
During a change of the solvent in an HPLC system, it is necessary for old solvent in the lines between the solvent bottles and the injection valve to likewise be flushed out via the waste port. Here, it is for example possible for the so-called injection needle to be moved directly over a waste container and for the contents of the line to be disposed of by way of the solvent pump(s). The disposal is generally referred to as “purge”. The abovementioned solvent change is described for example in U.S. Pat. No. 6,129,840 A.
If it is however sought to clean not only the sample delivery device but also the so-called needle seat, use is made, in known solutions, of a second solvent pump for cleaning purposes, as described for example in US 2013067997 A1.
In the prior art, therefore, only the lines from the solvent drawing-in lines to the switching valve, including the sample delivery device and the injection needle, but not the needle seat itself, are flushed through by means of the solvent pump(s). A further cleaning pump is consequently required for this purpose. Owing to the further pump, the construction becomes more complex and more expensive. If a further pump is omitted, contaminants in the needle seat must be accepted, which result in a so-called carry-over between the individually analyzed samples.
In the prior art, for the realization of the sample pre-compression and sample decompression, for the taking-in of the sample, for the sample injection and for the so-called purging, at least 3 grooves are provided in the stator or in the rotor of the injection valve in order to make it possible for corresponding switching positions to be realized. This has the result that the sealing surface between the connections becomes very small, leading to certain leakage rates. It would accordingly be advantageous to provide an injection valve which, by means of at most 2 grooves, makes it possible to realize all of the required switching states.
Furthermore, in the so-called injection position (INJECT position) of the injection valve, that is to say the position while the sample is transferred to the chromatography column, some connecting lines of a sampler are not fully flushed through. Most connections, formed in the manner of grooves in the stator or rotor of the injection valve, are required in order to be able to switch back and forth between the so-called loading position (LOAD position; introduction of the sample into a sample loop of the injection valve) and the pressure equalization position (PRESSURE EQUALIZATION position; position in which the sample loop is brought to the system pressure or ambient pressure), and also between the INJECT position and the PRESSURE EQUALIZATION position, without the solvent flow to the column being interrupted. The flow must not be interrupted because, otherwise, the pump pressure would rise to an extreme extent and the column pressure would drop. The former is a problem for safety reasons, and in the case of the latter, long equilibration phases are required between the sample analyses. The solvent used at the start of the chromatography run (for example in the equilibration phase) accumulates in said grooves and falsifies the gradient composition during the further process owing to the mixing of the solvent residue with the gradient (which is critical in particular in the case of low-flow/nano-flow applications).